Optimization of interlayer handovers in multilayer wireless communication networks

ABSTRACT

Technologies are described herein for parameter optimization of at least one interlayer handover in a multilayer wireless cellular communication network. Performance information for the communication network is retrieved. The retrieved performance information for the communication network is then averaged over a predetermined period of time. A determination is made based on the performance information as to whether optimization of the communication network is required. If so, the interlayer handover is optimized by capturing a current set of configuration parameters for the interlayer handover, generating a new set of configuration parameters for the interlayer handover based on the retrieved performance information and the current set of configuration parameters, and applying the new set of configuration parameters to the communication network.

BACKGROUND

Wireless cellular communications networks often divide the total set ofavailable channels into different groups, or “layers.” Layers within anetwork may belong to the same radio access technology. For instance,different layers can be defined as different sets of frequencies withina Global System for Mobile Communications (“GSM”) communicationsnetwork. It is also possible to have different layers served withdifferent radio access technologies. For instance, GSM and Wideband CodeDivision Multiple Access (“WCDMA”) layers can coexist within the samecommunications network. Wireless handsets connected to such wirelesscommunications networks may be transferred between layers using aninterlayer handover procedure that is triggered when a set of thresholdconditions is fulfilled. The set of interlayer handover thresholdconditions are typically defined by configuration parameters specifiedwithin the wireless communications network.

It can be very difficult and time consuming to optimize theconfiguration parameters that specify the interlayer handover thresholdconditions on a cell-by-cell basis in a large wireless cellularcommunications network. As a result, wireless operators frequentlyutilize a generic set of configuration parameters for all of the cellsites within a communications network. Utilization of a generic set ofconfiguration parameters in this manner, however, generally results insub-optimal performance in terms of both quality and capacity. Onereason for this is that interference and propagation severity can varyboth in time and space over a wireless network, which is not taken intoaccount when utilizing a generic set of configuration parameters acrossall cell sites.

Field trials may be performed in order to tune the configurationparameters for cell sites within a wireless communications network.However, the effects of modifying configuration parameters during thetuning process are difficult to quantify. As a result, the tunedconfiguration parameters are often selected conservatively, therebylimiting the achievable performance of the communications network.Moreover, such trials are normally focused on global parameters of oneor more features under study. Optimization is rarely performed on acell-by-cell basis due to the large associated cost. As a result, mostwireless cellular communications networks are unable to obtain peaklevels of quality and performance.

It is with respect to these considerations and others that thedisclosure made herein is presented.

SUMMARY

Technologies are described herein for optimizing interlayer handovers ina wireless cellular communications network. Through the utilization ofthe technologies and concepts presented herein, the configurationparameters that specify the interlayer handover threshold conditions ina multilayer wireless cellular communications network can be optimizedon a cell-by-cell basis to provide peak levels of quality andperformance. Moreover, the optimization of the configuration parameterscan be performed without the need for costly field trials.

According to one aspect, performance information is retrieved for amultilayer wireless cellular communication network. The performanceinformation may be retrieved, for instance, from an Operation andSupport System (“OSS”) operating within the network. According toimplementations, the performance information is identified by one ormore Key Performance Indicators (“KPIs”) of the network. For example,KPIs may include a carrier-to-carrier interference ratio (“C/I”), areceived signal level, a user speed level, or a path loss indicator. Theperformance information may also be identified by reported alarm eventsin the communication network.

The retrieved performance information is averaged over a predeterminedperiod of time. If the performance information indicates thatoptimization is required, an interlayer handover within the network maybe optimized by capturing a current set of configuration parameters forthe interlayer handover. A new set of configuration parameters are thengenerated based on the current set of configuration parameters and theretrieved performance information. The new set of configurationparameters is then applied to the communication network. This processmay be repeated for each cell and layer in the communication network.

According to additional aspects, the interlayer handover is operative tohand over a wireless communication from one layer of the network toanother layer in the network. The interlayer handover is triggered whenat least one threshold condition is fulfilled. The threshold conditionis defined by the current set of configuration parameters, describedabove.

In one implementation, the communication network includes a macrolayerthat presents at least one macrocell and a microlayer that presents atleast one microcell. In this implementation, generating the new set ofconfiguration parameters for the interlayer handover may includerelaxing a threshold condition for entering the microlayer whencongestion in the macrocell is detected and congestion or qualitydegradation are not detected in the microcell. Alternatively, generatingthe new set of configuration parameters may include increasing athreshold condition for entering the microlayer when quality orcongestion problems in the microcell are not detected.

In another implementation, the communication network includes at leasttwo layers operating at different frequencies. In this scenario, theinterlayer handover is a load based inter-frequency handover. Generatinga new set of configuration parameters for the interlayer handoverincludes monitoring a load in the two layers and adjusting a handoverload threshold condition in order to achieve a balanced distribution ofthe load between the two layers.

The above-described subject matter may also be implemented as acomputer-controlled apparatus, a computer process, a computing system,or as an article of manufacture such as a computer-readable medium.These and various other features will be apparent from a reading of thefollowing Detailed Description and a review of the associated drawings.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intendedthat this Summary be used to limit the scope of the claimed subjectmatter. Furthermore, the claimed subject matter is not limited toimplementations that solve any or all disadvantages noted in any part ofthis disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an illustrative operating environmentfor aspects of the various embodiments presented herein along withaspects of a system for optimizing interlayer handovers in a cellularcommunication network presented herein;

FIG. 2 is a flow chart illustrating one routine for parameteroptimization of interlayer handovers in a multilayer wireless cellularcommunication network according to one embodiment;

FIG. 3 is a schematic diagram illustrating a hierarchical macro andmicrocell structure of a multilayer wireless cellular communicationnetwork that forms an operating environment for embodiments presentedherein;

FIG. 4 is a schematic diagram illustrating a load based inter-frequencyhandover in a WCDMA communications network;

FIG. 5 is a schematic diagram illustrating a coverage basedinter-frequency handover in a WCDMA communications network; and

FIG. 6 is a computer architecture diagram showing an illustrativecomputer hardware and software architecture for a computing systemcapable of implementing the embodiments presented herein.

DETAILED DESCRIPTION

The following detailed description is directed to technologies foroptimizing interlayer handovers in a wireless cellular communicationsnetwork. While the subject matter described herein is presented in thegeneral context of program modules that execute in conjunction with theexecution of an operating system and application programs on a computersystem, those skilled in the art will recognize that otherimplementations may be performed in combination with other types ofprogram modules. Generally, program modules include routines, programs,components, data structures, and other types of structures that performparticular tasks or implement particular abstract data types. Moreover,those skilled in the art will appreciate that the subject matterdescribed herein may be practiced with other computer systemconfigurations, including hand-held devices, multiprocessor systems,microprocessor-based or programmable consumer electronics,minicomputers, mainframe computers, and the like.

In the following detailed description, references are made to theaccompanying drawings that form a part hereof, and which are shown byway of illustration specific embodiments or examples. Referring now tothe drawings, in which like numerals represent like elements through theseveral figures, aspects of a computing system and methodology foroptimizing interlayer handovers in a wireless cellular communicationsnetwork will be described.

Turning now to FIG. 1, details will be provided regarding one embodimentpresented herein for optimizing interlayer handovers in a wirelesscellular communications network. In particular, FIG. 1 is a blockdiagram showing an illustrative operating environment for aspects of thevarious embodiments presented herein along with aspects of a system foroptimizing interlayer handovers in a cellular communication networkpresented herein. In this implementation, KPIs and alarm events reportedwithin a communications network are utilized to derive modifications tothreshold conditions governing interlayer handovers. Details regardingthis process are provided below.

As can be seen in FIG. 1, a system 2 for optimizing interlayer handoversincludes an Operation and Support System (“OSS”) 4, and a tuning system6 for optimizing network performance, including the optimization of oneor more handover parameters 8. The system 2 shown in FIG. 1 is presentedin the context of a wireless communications network that presents threelayers 10A, 10B, and 10C. The layer 10C includes two cells 12A-12B, thelayer 10B includes one cell 12C, and the layer 10A includes one cell12D. Between the layers of the network there are interlayer handovers14A-14D to hand wireless communications from one layer to another layer.For example, the interlayer handover 14A is between the cells 12C and12D of the layers 10B and 10A, respectively. The interlayer handover 14Bis between the cells 12A and 12D of the layers 10C and 10A,respectively. The interlayer handover 14C is between the cells 12A and12C of the layers 10C and 10B, respectively. It should be appreciatedthat each cited interlayer handover 14 might comprise two interlayerhandovers, one for each direction. For instance, the handover 14Bcomprises a handover to hand users from cell 12D of layer 10A to cell12A of layer 10C and a handover to hand users from cell 12A to cell 12C.

In the wireless communications network shown in FIG. 1 each interlayerhandover 14 is triggered when a certain set of threshold conditions isfulfilled. The threshold conditions are defined by one or more handoverparameters 8. The tuning system 6 optimizes the handover parameters(also referred to herein as “configuration parameters”) utilizinginformation retrieved from the database 16 and a current set ofconfiguration parameters for the wireless communications network. Thedatabase 16 is maintained by the OSS 4 and stores information about theperformance of the communications network. In particular, this data isstored in the form of KPIs 18, reported alarms 20, and other data.Additional information may be stored in the database 16, such aspropagation data, drive-test data, and other types of data regarding theperformance of the wireless communications network. The database 16serves this information about the network performance to the tuningsystem 6.

As will be described in greater detail below, the tuning system 6utilizes the KPIs 18, alarms 20, and the current set of configurationparameters for the communications network to calculate a new set ofhandover parameters. The new handover parameters are intended tooptimize network performance according to a set of criteria that aretaken into account when designing the tuning system 6. The tuning system6 applies the new handover parameters to the communications network.

Turning now to FIG. 2, additional details will be provided regarding theembodiments presented herein for optimizing interlayer handovers in awireless communication network. In particular, FIG. 2 is a flow diagramshowing a routine 200 illustrating a method performed by the tuningsystem 6 for optimizing the parameters of an interlayer handover in amultilayer wireless cellular communication network according to oneimplementation provided herein. It should be appreciated that thelogical operations described herein are implemented (1) as a sequence ofcomputer implemented acts or program modules running on a computingsystem and/or (2) as interconnected machine logic circuits or circuitmodules within the computing system. The implementation is a matter ofchoice dependent on the performance and other requirements of thecomputing system. Accordingly, the logical operations described hereinare referred to variously as operations, structural devices, acts, ormodules. These operations, structural devices, acts and modules may beimplemented in software, in firmware, in special purpose digital logic,and any combination thereof. It should also be appreciated that more orfewer operations may be performed than shown in the figures anddescribed herein. These operations may also be performed in a differentorder than those described herein.

The routine 200 begins at operation 202, where the tuning system 6retrieves the KPIs 18 from the database 16. The alarms 20 may also beretrieved from the database 16 at operation 202. As discussed above,other information maintained by the OSS 4 may also be retrieved andutilized by the tuning system 6 in the generation of the new handoverparameters. From operation 202, the routine 200 continues to operation204, where the tuning system 6 averages the KPIs and other retrieveddata with similar data previously retrieved from the database 16. Itshould be appreciated that the retrieved information should be averagedover a sufficiently long period of time, so that statistical noise issuppressed. Due to the necessary averaging periods, the method issuitable for long-term optimization tasks (e.g. daily or weekly updatesof the system parameters). In this regard, the tuning system 6 may waita predetermined period of time prior to averaging new performance datafrom the database 16. Accordingly, the tuning system 6 determines atoperation 206 whether a pre-determined period of time has elapsed sincethe performance data was last averaged. If not, the routine 200 returnsto operation 202, described above. If the pre-determined period of timehas elapsed, the routine 200 continues to operation 208, where thetuning system 6 determines whether optimization of the communicationnetwork is required.

If optimization is not required, the routine 200 returns to operation202, described above. If optimization is required at operation 208, theroutine 200 continues to operation 210, where the current set ofhandover parameters 8 of the interlayer handover is captured served tothe tuning system 6. The routine 200 then continues to operation 212,where a new set of configuration parameters is determined by the tuningsystem 6. In particular, in one implementation the new set ofconfiguration parameters is generated utilizing the network performancedata retrieved from the database 16 and the current set of configurationparameters. Once the new set of handover parameters 8 have beengenerated, the new set of handover parameters is applied to the cell inthe wireless network in which the interlayer handover is defined. Oncethe new handover parameters have been applied to the network, theroutine 200 continues to operation 216, where it ends. It should beappreciated that the routine 200 illustrated in FIG. 2 may be appliedcontinuously and repeatedly for all interlayer handovers occurringwithin a wireless network to ensure that network performance iscontinually optimized.

FIG. 3 illustrates in a schematic diagram form how users are allocatedto different layers in one hierarchical multilayer cell structure. Inthis regard, it should be appreciated that a typical objective of themultilayer strategies in wireless cellular communication networks is toprovide continuous coverage with one layer, while increasing thecapacity with other layers. For example, in a GSM system, continuouscoverage is achieved by means of a layer with loose frequency reuse,while capacity is increased by using a tight frequency reuse in theother (insecure) layer. Of course, not all the users should access theinsecure layer, since this is meant for users close to the base station,which are the ones having enough signal quality to cope with theinterference situation created by the utilized frequency reuse. Ingeneral, the layer with loose frequency reuse, which is intended forcoverage provision, is called the macrolayer, and the cells in thislayer are called macrocells. Similarly, the insecure layer is called themicrolayer, and the cells in this layer are called microcells due totheir reduced dominance area.

The structure of a multilayer wireless cellular communication network300 shown in FIG. 3 comprises a microcell 302, a macrocell 304, and abase station 306. As can be seen, the handsets located near the basestation 306 are in the microcell 302 whereas handsets located furtheraway from the base station 306 are in the macrocell 304. The conditionthat has to be fulfilled in order to trigger the handover of a usertowards the microcell 302 is typically defined as the minimumcarrier-to-interference ratio (“C/I”) that has to be experienced by ahandset. Instead of the C/I, other alternative measures can be alsoutilized, such as the path loss and the received signal level, amongothers. Equivalent criteria must also be defined for handing handsetsover to the macrocell 304. Among others, these criteria can be based onC/I, path loss or quality measures.

In addition to the signal quality criteria, it is also desirable to keepfast moving handsets in the macrolayer provided by the macrocell 304,since the small size of the microcell 302 would generate an excessivenumber of handovers. For this purpose, a corresponding speed relatedthreshold has to be defined and adjusted. Within this framework, areasonable approach for threshold definition is to try to push as muchtraffic as possible towards the microlayer provided by the microcell302, provided that no congestion or quality problems appear in thislayer. The manner to push traffic towards the microlayer provided by themicrocell 302 is to relax the threshold conditions that must befulfilled in order to have a handset handed over to that layer. In thiscontext, quality can be defined in terms of, for example, dropped callrate, and/or handover failure rate. When defining the congestion in acertain layer, this can be done, for example, in terms of call blockingrate and/or percentage of utilized transmission resources during acertain period (e.g. the busy hour).

In view of the above, an optimization algorithm utilized by the tuningsystem 6 in one implementation utilizes two rules: 1) the thresholdcondition for entering a microlayer is relaxed (which is equivalent topushing traffic towards the microlayer) when there is congestion in themacrocell 304 and there are no congestion or quality problems in themicrocell 302 and 2) the threshold conditions for entering a microlayerare made more demanding (which is equivalent to pushing traffic towardsthe macrolayer) when there are quality or congestion problems in themicrolayer. In this context, relaxing a threshold condition for enteringa cell means modifying the threshold so that more users can enter thecell. If the threshold condition is defined in terms of C/I, thisrelaxation operation involves a reduction of the C/I thresholdcondition.

FIG. 4 illustrates in a schematic diagram form a network 400 in whichseveral WCDMA layers 402A-402B with equal planned dominance area aredeployed. The layers 402A-402B coexist and load-based interlayerhandovers are possible in order to balance the load at the differentcells. The network 400 comprises a first layer 402A operating at a firstfrequency that presents a first cell 12E and a second cell 12F. Thenetwork 400 also includes a second layer 402B operating at a secondfrequency that presents a first cell 12G and a second cell 12H.

The network configuration illustrated in FIG. 4 may comprise amultilayer WCDMA network in which each of the layers 402A-402B isidentified by the use of a different frequency. Different mechanisms maybe utilized to deploy such a multilayer structure. For instance, highcapacity sites operating at different frequencies can be built, whichimplies that traffic balance operations between both layers can be basedon load measures at each layer, with the subsequent load definitions interms of system throughput, transmitted or received power or number ofusers, throughput per user and queuing time statistics, among others. Inthis case, no distinction between macrocells and microcells is made,since no different dominance area is planned for each type of cell.Typically, this kind of multi carrier site will be initially deployedonly in regions with high offered traffic.

In the network shown in FIG. 4, several threshold optimizationstrategies can be designed in different embodiments. In general, loadbased inter-frequency handovers 14E-14F are triggered when the load inthe current cell exceeds a certain threshold. However, it is notdesirable to start these handover procedures towards cells that are moreloaded than the current cell. Similarly, it is also undesirable to havethe traffic unevenly distributed among the different layers. Thus, onepossible optimization strategy to implement by the tuning system 6 is tomonitor the load in both of the layers 402A-402B and to adjust thehandover parameters 8 in order to achieve a balanced distribution of thetraffic among the layers 402A-402B.

Another manner to deploy a multilayer structure in WCDMA is to enablemacro and microcells. As in the GSM system, continuous coverage will beprovided with macrocells, while microcells will be deployed for capacityenhancement. In the WCDMA case, the same frequency reuse is used in eachlayer, though different transmit powers can be applied at differentlayers, with the subsequent difference in the coverage range. Due to thesame reasons that were pointed out above with respect to the GSM case,it is also possible to keep fast moving handsets in the macrolayer,which also requires the definition and adjustment of the correspondingspeed related threshold. In this case, it is possible for the tuningsystem 6 to use the same optimization strategies as in the GSM case(i.e. the system can try to push as much traffic as possible towards themicrolayer, provided that no quality or congestion problems appear inthis layer).

The definition of layers associated to different radio accesstechnologies is also a realistic scenario. At the start of WCDMAdeployment, this radio access technology will not provide full coverage.Thus, handovers from WCDMA to GSM will be a widely used method toguarantee continuous coverage. Moreover, load-based handovers in bothdirections will be useful in order to balance the load of both systems,taking into account that not all services can be provided over bothradio access technologies. These transition policies will be translatedinto some rules and criteria, which will depend on thresholds that haveto be compared with some measures in order to make a handover decision.Like in the aforementioned cases, the adjustment of the inter-systemhandover thresholds will be done, by the tuning system 6, in a way thatcauses as much traffic as possible to be pushed toward the desiredsystem, provided that no quality or congestion problems are caused.

FIG. 5 illustrates in a schematic diagram form a situation in which thecoverage with one of the WCDMA layers is discontinued, which forces aninter-frequency handover operation in order to guarantee mobility. Thenetwork 500 shown in FIG. 5 comprises a first layer 502 that presentsthree cells 12I-12K, and a second layer 504 that presents two cells12L-12M. The layers 502 and 504 operate at different frequencies. In theexample network shown in FIG. 5, multi carrier sites will be initiallydeployed only in regions with high offered traffic. Thus, when movingaway from that region, it is likely that the coverage with some of thefrequencies is discontinued. In that case, an inter-frequency handover14H will be executed due to coverage reasons. For this operation, thetuning system 6 must define a threshold based on, for example, thequality of the received pilot signals from each cell. In particular, aninterlayer handover 14H is triggered and the handsets are handed fromthe cell 12M of layer 504 to the cell 12K of the layer 502 because thecoverage with the frequency used in the layer 504 is discontinued.

FIG. 6 shows an illustrative computer architecture for a computer 600capable of executing the software components described herein. Inparticular, the computer 600 may be utilized in the tuning system 6 toexecute a tuning application program 622 capable of performing thesoftware operations described herein for optimizing a wirelesscommunication network. The computer architecture shown in FIG. 6illustrates a conventional desktop, laptop computer, or server computerand may be utilized to execute any aspects of the methods presentedherein for optimizing a wireless network.

The computer architecture shown in FIG. 6 includes a central processingunit 602 (“CPU”), a system memory 608, including a random access memory614 (“RAM”) and a read-only memory (“ROM”) 616, and a system bus 604that couples the memory to the CPU 602. A basic input/output systemcontaining the basic routines that help to transfer information betweenelements within the computer 600, such as during startup, is stored inthe ROM 616. The computer 600 further includes a mass storage device 610for storing an operating system 618, application programs, and otherprogram modules, which will be described in greater detail below.

The mass storage device 610 is connected to the CPU 602 through a massstorage controller (not shown) connected to the bus 604. The massstorage device 610 and its associated computer-readable media providenon-volatile storage for the computer 600. Although the description ofcomputer-readable media contained herein refers to a mass storagedevice, such as a hard disk or CD-ROM drive, it should be appreciated bythose skilled in the art that computer-readable media can be anyavailable computer storage media that can be accessed by the computer600.

By way of example, and not limitation, computer-readable media mayinclude volatile and non-volatile, removable and non-removable mediaimplemented in any method or technology for storage of information suchas computer-readable instructions, data structures, program modules orother data. For example, computer-readable media includes, but is notlimited to, RAM, ROM, EPROM, EEPROM, flash memory or other solid statememory technology, CD-ROM, digital versatile disks (“DVD”), HD-DVD,BLU-RAY, or other optical storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium which can be used to store the desired information and which canbe accessed by the computer 600.

According to various embodiments, the computer 600 may operate in anetworked environment using logical connections to remote computersthrough a network such as the network 620. The computer 600 may connectto the network 620 through a network interface unit 606 connected to thebus 604. It should be appreciated that the network interface unit 606may also be utilized to connect to other types of networks and remotecomputer systems. The computer 600 may also include an input/outputcontroller 612 for receiving and processing input from a number of otherdevices, including a keyboard, mouse, or electronic stylus (not shown inFIG. 6). Similarly, an input/output controller may provide output to adisplay screen, a printer, or other type of output device (also notshown in FIG. 6).

As mentioned briefly above, a number of program modules and data filesmay be stored in the mass storage device 610 and RAM 614 of the computer600, including an operating system 618 suitable for controlling theoperation of a networked desktop, laptop, or server computer. The massstorage device 610 and RAM 614 may also store one or more programmodules. In particular, the mass storage device 610 and the RAM 614 maystore a tuning application program 622 that provides the functionalitydescribed herein for optimizing a wireless communication network. Otherprogram modules and data may also be stored on the mass storage device610 and in the RAM 614.

Based on the foregoing, it should be appreciated that technologies forparameter optimization of at least one interlayer handover in amultilayer wireless cellular communication network are presented herein.Although the subject matter presented herein has been described inlanguage specific to computer structural features, methodological acts,and computer readable media, it is to be understood that the inventiondefined in the appended claims is not necessarily limited to thespecific features, acts, or media described herein. Rather, the specificfeatures, acts and mediums are disclosed as example forms ofimplementing the claims.

The subject matter described above is provided by way of illustrationonly and should not be construed as limiting. Various modifications andchanges may be made to the subject matter described herein withoutfollowing the example embodiments and applications illustrated anddescribed, and without departing from the true spirit and scope of thepresent invention, which is set forth in the following claims.

What is claimed is:
 1. A method for parameter optimization of at least one interlayer handover in a multilayer wireless cellular communication network, the method comprising: retrieving performance information for the communication network, wherein the communication network comprises a macrolayer that presents at least one macrocell and a microlayer that presents at least one microcell; averaging the retrieved performance information for the communication network over a predetermined period of time; determining based on the averaged performance information whether optimization of the communication network is required; and in response to determining that optimization of the communication network is required, optimizing the interlayer handover by capturing a current set of configuration parameters for the interlayer handover, generating a new set of configuration parameters for the interlayer handover based on the retrieved performance information and the current set of configuration parameters by relaxing a threshold condition for entering the microlayer when congestion in the macrocell is detected and congestion or quality degradation are not detected in the microcell, and applying the new set of configuration parameters to the communication network.
 2. The method of claim 1, wherein the multilayer wireless cellular communication network comprises a plurality of cells and a plurality of layers, and wherein the retrieving, averaging, determining, and optimizing operations are performed for each cell of each layer of the communication network.
 3. The method of claim 2, wherein the performance information comprises data identifying one or more Key Performance Indicators (KPIs) of the communication network.
 4. The method of claim 3, wherein the performance information comprises data identifying one or more reported alarm events in the communication network, and wherein generating a new set of configuration parameters for the interlayer handover comprises generating a new set of configuration parameters for the interlayer handover based on the data identifying one or more reported alarm events in the communication network.
 5. The method of claim 4, wherein the communication network further comprises an Operation and Support System (OSS), and wherein retrieving performance information for the communication network comprises retrieving the performance information from the OSS.
 6. The method of claim 5, wherein the interlayer handover is operative to hand over a wireless communication from a first layer to a second layer of the communication network.
 7. The method of claim 6, wherein the interlayer handover is triggered when at least one threshold condition is fulfilled.
 8. The method of claim 7, wherein the threshold condition is defined by the current set of configuration parameters.
 9. The method of claim 8, wherein the KPIs comprise one or more of a carrier-to-carrier interference ratio (C/I), a received signal level, a user speed level, or a path loss indicator, and wherein the threshold condition is defined by at least one of the KPIs.
 10. The method of claim 9, wherein the communication network comprises at least two layers operating at different frequencies and the interlayer handover is a load based inter-frequency handover, and wherein generating a new set of configuration parameters for the interlayer handover comprises monitoring a load in the two layers and adjusting a handover load threshold condition in order to achieve a balanced distribution of the load among the two layers.
 11. The method of claim 1, wherein generating a new set of configuration parameters for the interlayer handover based on the retrieved performance information and the current set of configuration parameters comprises increasing a threshold condition for entering the microlayer when quality or congestion problems in the microcell are not detected.
 12. A system for parameter optimization of at least one interlayer handover in a multilayer wireless cellular communication network comprising a macrolayer that presents at least one macrocell and a microlayer that presents at least one microcell, the system comprising: a tuning system configured to retrieve information about the network performance, average the retrieved information about the network performance over a predetermined period of time, receive a current set of configuration parameters for the interlayer handover that are captured from the network, determine a new set of configuration parameters for the interlayer handover according to at least one criterion, on the basis of the retrieved information about the network performance, and the captured current set of configuration parameters for the interlayer handover by relaxing a threshold condition for entering the microlayer when congestion in the macrocell is detected and congestion or quality degradation are not detected in the microcell, and to cause the determined new set of configuration parameters for the interlayer handover to be applied to the communication network.
 13. The system of claim 12, wherein the information about the network performance comprises one or more Key Performance Indicators (KPIs) of the communication network.
 14. The system of claim 13, wherein the information about the network performance comprises data identifying one or more reported alarm events in the communication network.
 15. The system of claim 14, wherein the interlayer handover is operative to hand over a wireless communication from a first layer to a second layer of the communication network.
 16. The system of claim 15, wherein the interlayer handover is triggered when at least one threshold condition is fulfilled, the threshold condition being defined by the captured current set of configuration parameters.
 17. The system of claim 16, wherein the KPIs comprise one or more of a carrier-to-carrier interference ratio (C/I), a received signal level, a user speed level, or a path loss indicator, and wherein the threshold condition is defined by at least one of the KPIs.
 18. A computer-readable storage medium that is not a signal comprising computer-executable instructions stored thereon, which, when executed by a computer, cause the computer to: retrieve performance information for a communication network comprising a macrolayer that presents at least one macrocell and a microlayer that presents at least one microcell; take an average of the retrieved performance information for the communication network over a predetermined period of time; determine based on the averaged performance information whether optimization of the communication network is required; and in response to determining that optimization of the communication network is required, optimize an interlayer handover by capturing a current set of configuration parameters for the interlayer handover, generating a new set of configuration parameters for the interlayer handover based on the retrieved performance information and the current set of configuration parameters by relaxing a threshold condition for entering the microlayer when congestion in the macrocell is detected and congestion or quality degradation are not detected in the microcell, and applying the new set of configuration parameters to the communication network. 